This invention relates to a pickup device for deriving a measurable voltage which is a linear function of the magnitude of pulsating high voltage in an insulated conductor, and more particularly to such a pickup device of the capacitive type for pulsating voltages of the order of 15 to 40 kilovolts.
The pickup device of the invention has been developed for use in testing apparatus, particularly testing apparatus for trouble shooting work on the ignition system of internal combustion engines. While apparatus with which the pickup device is used may be capable of making tests in the low voltage portions of the ignition system, the present capacitive pickup device is used only in connection with making tests in the high voltage portions, for example, the cable leading from the coil to the distributor of the engine and the cables leading from the distributor to the respective spark plugs.
One object of the invention is to provide a capacitive pickup device for use with an insulated conductor of pulsating high voltage, the device providing a measurable voltage which is a linear function of the magnitude of the voltage on the conductor.
Another object of the invention is to provide a capacitive pickup device capable of being applied to and removed from a high voltage conductor without the need for disconnecting either end of the conductor.
Still another object of the invention is to provide a capacitive pickup device having electrical features that cooperate to minimize the fringing effects of extraneous electric fields which otherwise would introduce error in voltage applied by the device to associated testing apparatus.
Applicant does not know of any comparable capacitive pickup device prior to the present invention.